1. Field
This invention relates to improvements in the art of adaptive signal processing, particularly as applied to adaptive filters and more specifically to antenna systems that discriminate directionally against interference by adaptively forming suitable directive patterns.
2. Prior Art
Adaptive antenna systems are described in the following references:
B. Widrow et al., "Adaptive Antenna Systems", Proc. IEEE, Vol. 56 pp 2143-2159 (December 1967)
L. J. Griffiths, "A Simple Adaptive Algorithm for Real-Time Processing in Antenna Arrays" Proc. IEEE, Vol. 57, pp 1696-1704, (October 1969)
C. Giraudon, "Adaptive Antenna Processing", U.S. Pat. No. 3,876,947.
The Giraudon system, although evidently an improvement over its acknowledged predecessors, is quite complex, requires prior knowledge of the direction of arrival of the desired signal and its frequency in order to operate, and is restricted to narrow band useful signals.
The Widrow et al. and the Griffiths system require either prior knowledge of the direction of arrival or else a replica waveform duplicating the desired signal. Both of these systems, and other known iteratively adaptive systems, tend to null relatively quickly on strong interference sources and relatively slowly on weaker but still significant sources, so that the settling time in some signal environments is undesirably long.
Another problem with prior art systems is the provision of sufficient dynamic range capability to avoid suppression of a desired weak signal due to saturation of active elements, such as amplifiers, by relatively strong interference.